Container handling

Sensors in the Rotterdam container terminal
Modern up to 400 m long container ships can transport much over 10,000 containers. Complex technology ensures trouble-free loading and unloading.

Every year over 430 million tons of cargo are handled in the largest port in Europe. A sophisticated technology ensures smooth logistics. Sensors provide the required pulses.

More than 34,000 sea-going ships and 100,000 ships on inland waterways arrive at the port of Rotterdam every year. The huge container terminal is located in Maasvlakte, an area of the port directly on the North Sea where 6.7 million containers were handled in 2010. But when you expect hustle and bustle in this area you are wrong. You hardly see any people there. As if controlled by magic, giant dockside cranes lift the containers from the ship and put them on AGVs every minute.

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Every minute the containers are put on the AGVs which transport them to the stacking yard.

These AGVs look like trucks without a cab. And in fact these vehicles move without drivers. Instead, a PLC for mobile applications controls the vehicles by means of sensors.

The AGVs transport the containers from the dockside crane to the stacking yard. There, stacker cranes pick the containers and stack them in the storage area. What may look chaotic to ordinary persons is done systematically: The logistics computer exactly knows where to position each container. Depending on the storage time - often only a few hours - the containers are stacked following an optimised pattern to ensure an efficient and trouble-free operation. This is necessary because the schedules in international container handling are very tight. Every minute of delay costs money. Therefore the technology must always function - when it is icy cold, hot in summer and also in stormy and rainy North Sea weather.

Lifting gear
Spreaders play a major role in container handling. This is a lifting gear which grips the containers from the top. These telescopic frames can be set to the different container lengths and are used for dockside and stacker cranes.

The lifting gear which grips the containers from the top is called spreader. 40 inductive sensors monitor the automatic gripping process.

The spreaders are fitted with bolts in the corners which engage into the upper fittings of the containers and are then turned by 90 degrees (also called twistlock). This ensures that the container is secured and can be lifted off safely.

Twistlock: In the four corners the spreaders are fitted with bolts whose lower end is turned by 90 degrees to ensure that the container is secured.

For automating this process and monitoring the twistlock 40 inductive sensors from ifm electronic are used for every spreader.

When the spreader is positioned on the container, guide brackets at the corners - called flippers - guide the spreader into place. At different positions of the spreader bolts are attached which are lifted when the gear lies flat on the container. So, a canted spreader position on the container roof would be detected reliably. Inductive sensors are used to detect these bolts. The signal for locking is not triggered until all bolts are completely lifted.

To be on the safe side, inductive sensors are used again. They check the orientation of the twistlock bolts. This ensures that the container is in fact secured at all four corners before it is lifted off.

In every corner of the spreader: The left inductive sensor monitors the bolt which is lifted when the spreader lies flat on the container. The two sensors on the right monitor the 90-degree turn of the twistlock.

Locking and moving the flippers are done hydraulically. Pressure and temperature of the hydraulics are monitored using sensors for mobile machines from ifm electronic. All sensors on the spreader are connected via the AS-Interface bus system. 17 slaves are used as I/O modules, which ensures simple and well-arranged wiring.

In the control cabinet of the spreader all sensor signals are connected to AS-i I/O modules.

Well positioned
As if controlled by magic, the AGVs transport the containers from the dockside crane to the stacking yard. A central computer determines the loading and unloading points as well as the container's progress through the port and transmits this information to the AGVs via radio. Induction loops in the ground and numerous sensors ensure that navigation is precise to the nearest centimetre.

Computer-controlled: Thanks to state-of-the-art control technology and sensors the AGVs automatically find their way to the stacker cranes.

Two mobile controllers (ecomatmobile R360 safety controllers) from ifm electronic are at the heart of these vehicles. They are specifically designed for severe operating conditions. Their high protection rating as well as the wide temperature and operating voltage range provide maximum safety. They communicate with the robust full-metal I/O modules to which the sensors are connected via CANbus.

The heart of the AGVs is the ecomatmobile R360 controller from ifm electronic. The PDM360 display provides clear status and diagnostic information.

A PDM display is installed in the control cabinet on the side of the vehicle. It provides clear status and diagnostic information.

ifm pressure sensors monitor the hydraulics of the AGVs. Temperature sensors are used to monitor the hydraulics and the control cabinet. Inductive sensors at the bumpers detect a collision and stop the vehicle without delay. ifm encoders monitor the steering.

Several sensors for mobile applications are mounted on the outside of the AGV. Here an ifm pressure sensor for monitoring the hydraulics.

Reliable connection
Complex electronics and a lot of sensors ensure the correct function of the spreaders. For a reliable transmission of the sensor signals ifm electronic developed an M12 connector that functions reliably under these harsh operating conditions. The system is permanently exposed to temperature fluctuations, moisture, dirt, corrosion, shock and vibration. The unique ecolink M12 connectors operate reliably in this difficult application.

A special feature is the robust locking of the screw connection. The asymmetric principle - "Easy to fasten and difficult to open!" - ensures sealing with long-term stability. This is important for thousands of sensor signals every day.

Conclusion
Everything in container handling must be done quickly, safely and reliably, otherwise the tight schedule of the container carriers cannot be maintained. It gives users a good feeling to know that they can rely on the safe function of ifm sensors, control systems and connection technology. Only this ensures full speed ahead!